Memory devices and/or imaging devices can be provided as internal, semiconductor, integrated circuits in computers or other electronic devices, e.g., cameras, or cell phones, among various other devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory, among others. There are also many different types of imagers including charge coupled device (CCD) imagers and complimentary metal oxide semiconductor (CMOS) imagers, among other imagers and/or image sensors.
Many memory devices include an array of memory cells arranged in rows and columns, while many imaging devices include an array of pixels arranged in rows and columns. Driver circuitry, e.g., a row/wordline driver, can be used to drive a row of pixels or a wordline to various voltages to perform various functions.
For example, in a flash memory device, a wordline driver can be used to apply various positive and negative voltages to wordlines in order to read, erase, refresh, and/or write data into the memory cell array. A row driver can be used to drive a row select signal or a row reset signal to various voltage levels in order to select the pixels in a row or to reset the pixels in a row, for example.
The various voltage levels to which a row/wordline driver output can be driven can be provided by various available voltage sources including external power supplies and/or internal voltage sources, among other voltage sources. The internal sources may include boost circuits that can provide positive and/or negative boost voltages to a driver. Boost circuits may be capacitively coupled which may cause boost voltages to be charge sensitive. As such, switching from a first voltage to a boosted voltage can put strain on a booster circuit in the form of charge depletion and/or current surge noise due to the presence of capacitive coupling.
Current row/wordline driver implementations can include level shifters that can be used to switch the driver output between two voltage levels. In such implementations, a multiplexer can be used to switch the driver output signal outside of the array to drive the output signal from an external power supply voltage to a boosted voltage.
However, switching outside the array can put strain on booster circuits since the booster circuit may drive a highly capacitive power wire that may go across all rows, level shifters for all rows, and a driver output signal for a row to receive the boost voltage. One such driver implementation is described in U.S. Pat. No. 5,668,758 entitled “Decode Wordline Driver with Positive and Negative Voltage Modes” to Yiu et al., which describes a wordline driver for a flash memory array.
Therefore, many row/wordline drivers may not provide drive outputs in a manner that adequately and/or efficiently switches between available voltage sources.